The aim of this study are to generate hybridization probes for a 44 kDal bone phosphoprotein (44K BPP, or osteopontin), to use these probes in studies on the 44K BPP gene, and to measure the effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on its gene expression. The overall objective of this study is to gain insight into the events involved in the control and regulation osteogenesis. The fundamental hypotheses on which these studies are based are that noncollagenous proteins (NCPs) are involved in the formation of bone and that the ROS 17/2.8 osteoblast-like osteosarcoma cell line is a suitable model for studying the biosynthesis and modulation of NCPs of bone by various hormones, including 1,25(OH)2D3. Previous studies have shown that ROS 17/2.8 cells synthesize and secrete 44K BPP, and that 1,25(OH)2D3 causes a dose related increase in the biosynthesis and secretion of 44K BPP. The data also indicate that this modulation probably occurs at the level of transcription. Clarification of these observations requires measurement of mRNA levels. Thus, the specific aims of the proposed studies are: 1. To obtain cDNA clones to the 44K BPP cDNA library for use in structural analysis of the gene and as hybridization probes. 2. To use a cDNA probe to the 44K BPP to compare the mRNA and genomic DNA from cells derived from normal rat bone and ROS 17/2.8 cells to assess the suitability of ROS cells for studying the biosynthesis and modulation of NCPs by 1,25(OH)2D3, and 3. To measure qualitative and quantitative effects of the hormone, 1,25(OH)2D3, on the transcription of specific mRNA(s) corresponding to the 44K BPP in rat calvaria organ cultures, osteoblasts, and ROS 17/2.8 cells. The information and reagents generated by these experiments will provide the essential foundation for further studies directed towards the elucidation of the mechanisms involved in the control and regulation of the expression of the 44K BPP gene by 1,25(OH)2D3. In turn, this will provide further understanding of the factors which may influence the osteogenic potential of the residual alveolar ridge. The development of successful regimens to maintain and/or augment the alveolar ridge, as well as the fabrication of more functional and aesthetic prosthetic devices is predicated on a more thorough understanding of the factors regulating bone formation.